1. Field of the Invention
This invention relates to laminated glass articles, more particularly, to bilayer laminated safety glass comprising a polycarbonate urethane adhered to a sheet of glass.
2. Brief Description of the Prior Art
Safety glass is a well-known term for a glass sandwich composed of a plastic interlayer bonding together two glass plates or sheets so that the breaking of the glass results in minimum dispersion of fragments of broken glass. Laminated safety glass is widely used in automobiles and must possess a number of properties including: (1) high impact energy absorption to minimize concussive injury; (2) shear and tear strength sufficient to prevent rupture of the interlayer by broken glass; (3) sufficient adhesion between the interlayer and the glass to prevent dispersion of broken glass to minimize lacerative injury; and (4) good optical quality.
One difficulty encountered in present windshields is that upon breaking, sharp glass edges may develop which may then cause severe laceration. Bilayer windshields comprising an outer ply of glass and an inner ply of plastic have been suggested for minimizing lacerative injury. However, since the plastic layer will be exposed to the atmosphere, it must have, in addition to the properties enumerated above, good weathering properties, such as ultraviolet light and hydrolytic stability, in order to retain its desirable mechanical properties and optical quality.
Since about 1930, plasticized polyvinyl butyral has been the most widely used interlayer material. However, it has been used almost exclusively in conventional trilayer windshields. Polyvinyl butyral is particularly susceptible to moisture and is not amenable to fabrication in the form of a bilayer windshield in which a surface of the polyvinyl butyral is exposed to the atmosphere.
There has been a trend in recent years to provide a substitute plastic interlayer material for polyvinyl butyral. U.S. Pat. Nos. 3,388,032; 3,522,142 and 3,620,950 and Belgian Pat. No. 785,125 all disclose various polyurethane materials for use in fabricating motor vehicle safety glass. The polyurethane materials, in general, offer improved physical properties over the polyvinyl butyral in that they have better impact resistance at high tempratures and are not nearly so moisture sensitive.
U.S. Pat. No. 3,764,457 entitled "Transparent Impact Resistant Poly(Carbonate-Urethane) Laminate" to Chang et al. and assigned to PPG Industries, Inc., the assignee of the instant invention, discloses that polycarbonate urethanes, particularly polyoxyalkylenecarbonate urethanes, are useful as inerlayers for safety glass windshields. The polycarbonate urethanes therein are prepared by the reaction of a diisocyante, an active hydrogen compound and a hydroxy-terminated aliphatic polycarbonate having ether linkages. The preferred polycarbonates are prepared from (1) carbon dioxide and 1,2-epoxides, (2) cyclic carbonates such as ethylene carbonate or (3) cyclic carbonates and a 1,2-epoxide. However, the ultraviolet light sensitivity of polyoxyalkylenecarbonate urethanes curtails their usefulness in bilayer laminates. Other methods are disclosed by which polycarbonates without ether linkages can be prepared, such as by the transesterification reaction of ethylene, propylene or diethylene glycols and dimethyl, diethyl or diphenyl carbonates.
In U.S. Pat. No. 3,544,524 entitled "Polyurethane Polymers Prepared From a Chain Extender and the Transesterification Product of 1,6-Hexanediol with a Diaryl Carbonate"to to Muller et al., polycarbonates of molecular weight 800 to 3000 are preferably prepared by the transesterification reaction of 1,6-hexanediol and diphenylcarbonate with removal of phenol by distillation. Muller et al. disclose that if polycarbonates are prepared by reacting 1,6-hexanediol with a dialkylcarbonate, the alkaline or acid ester interchange catalyst remains in the finished polycarbonate and adversely affects the quality of the polyurethane produced.
U.S. Pat. No. 2,789,966 entitled "Interpolycarbonates From 4,4'-bis(hydroxymethyl)-Biphenyl-bis(Alkyl or Aryl Carbonates)" to Reynolds et al. discloses novel interpolycarbonates prepared by co-condensing a primary bis-(carbonate) monomer having the formula ##STR1## and a copolymerizable bis-(carbonate) monomer having one of the following formulae: ##STR2## wherein R.sub.1 and R.sub.2 each represents an alkyl radical containing 1 to 4 carbon atoms or an aryl radical containing 6 to 8 carbon atoms and R.sub.3 represents an alkylene radical containing 4 to 10 carbon atoms, in the presence of a catalyst selected from Ti(OR).sub.4 and ether complexes of TiX.sub.4 wherein R represents an alkyl radical containing 1 to 18 carbon atoms and X represents a halogen. Reynolds et al. disclose the unusual advantages of employing a titanium catalyst where the primary bis-(carbonate) monomer and various copolymerizable bis-(carbonate) monomers yield interpolycarbonates which decompose in the presence of most ester-interchange catalysts.
In U.S. Pat. No. 3,379,693 entitled "Carbonate Compositions" Hostettler et al. disclose that novel carbonate compositions, 4-nitro-4 hydrocarbyloxymethyl - 2,6 dioxacyclohexanones, may be prepared by an aldol-like condensation of nitrosomethane and formaldehyde to produce tris-(hydroxymethyl)-nitromethane, which is then contacted with a halide (RX) to form a monoetherified product ##STR3## which can be reacted with a dialkyl carbonate in the presence of a titanate to form the novel compound ##STR4## Such cyclic carbonates are polymerized by ring-opening and chain addition. The polycarbonates so formed may be reacted with organic polyisocyanates to form polyurethanes useful as printing rollers, solid tires, and mechanical goods such as gears, seals, O-rings and shoe heels.